Question

我发现这个写得很好的如何使用AES加密的例子，我承认一些更高级的方面超出了我的范围。如果我使用相同的实例对象，该类工作正常。如果我使用完全相同的passPhrase创建另一个对象 - 该对象无法再正确解码上一个对象创建的任何类型的字符串或数据。我只能得出结论，因为这段代码采用了相当弱的passPhrase字符串，混合了SALT，并构建了一个更强的128位密钥 - 这个密钥构造过程每次都以某种方式随机化。意义是：

new AESEncrypter("MyPassword") <> new AESEncrypter("MyPassword")

有人可以帮我修改下面的课程以获得所需的行为：

AESEncrypter a = new AESEncrypter("MyPassword")
String encoded = a.encrypt("my message")

AESEncrypter b = new AESEncrypter("MyPassword")
b.decrypt(encoded) == "my message"

import java.security.spec.KeySpec;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;
import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class AESEncrypter {

    private static final byte[] SALT = {
            (byte) 0xA9, (byte) 0x9B, (byte) 0xC8, (byte) 0x32,
            (byte) 0x56, (byte) 0x35, (byte) 0xE3, (byte) 0x03
    };
    private static final int ITERATION_COUNT = 65536;
    private static final int KEY_LENGTH = 128;
    public Cipher ecipher;
    public Cipher dcipher;

    AESEncrypter(String passPhrase) throws Exception {

    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
        KeySpec spec = new PBEKeySpec(passPhrase.toCharArray(), SALT, ITERATION_COUNT, KEY_LENGTH);
        SecretKey tmp = factory.generateSecret(spec);

        // I Think the problem is here???

        SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");

        ecipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        ecipher.init(Cipher.ENCRYPT_MODE, secret);

        dcipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        byte[] iv = ecipher.getParameters().getParameterSpec(IvParameterSpec.class).getIV();
        dcipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iv));
    }

    public String encrypt(String encrypt) throws Exception {
        byte[] bytes = encrypt.getBytes("UTF8");
        byte[] encrypted = encrypt(bytes);
        return new BASE64Encoder().encode(encrypted);
    }

    public byte[] encrypt(byte[] plain) throws Exception {
        return ecipher.doFinal(plain);
    }

    public String decrypt(String encrypt) throws Exception {
        byte[] bytes = new BASE64Decoder().decodeBuffer(encrypt);
        byte[] decrypted = decrypt(bytes);
        return new String(decrypted, "UTF8");
    }

    public byte[] decrypt(byte[] encrypt) throws Exception {
        return dcipher.doFinal(encrypt);
    }

   public static void main(String[] args) throws Exception {

        String message = "MESSAGE";
        String password = "PASSWORD";

        AESEncrypter encrypter1 = new AESEncrypter(password);
        AESEncrypter encrypter2 = new AESEncrypter(password);

        String encrypted1 = encrypter1.encrypt(message);
        String encrypted2 = encrypter2.encrypt(message);

        System.out.println("Display Encrypted from object 1 and 2..why do they differ?" );

        System.out.println(encrypted1) ;
        System.out.println(encrypted2) ;

        System.out.println("Display Each object decrypting its own encrypted msg. Works as expected" );

        System.out.println(encrypter1.decrypt(encrypted1)) ;
        System.out.println(encrypter2.decrypt(encrypted2)) ;

        System.out.println("Attempt to decrypt the each others msg.. will fail" );

        System.out.println(encrypter1.decrypt(encrypted2)) ;
        System.out.println(encrypter2.decrypt(encrypted1)) ;

    }

}

显示从对象1和2加密..为什么它们不同？

drGy+BNSHPy34NWkkcNqLQ==

9p06VfBgTuh7TizZSbvKjw==

显示每个对象解密自己的加密消息。按预期工作

MESSAGE

MESSAGE

尝试解密彼此msg ..将失败

错误：

Exception in thread "main" javax.crypto.BadPaddingException: Given final block not properly padded
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:966)
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:824)
    at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:436)
    at javax.crypto.Cipher.doFinal(Cipher.java:2165)

Answer 1

问题在于，当您在CBC模式下初始化新的Cipher时，它会为您生成一个新的随机IV。这个初始化向量不必是秘密的，但它必须是不可预测的，以提供语义安全性。您只需将IV放在密文前面并用它进行解密即可。

public byte[] encrypt(byte[] plain) throws Exception {
    byte[] iv = ecipher.getParameters().getParameterSpec(IvParameterSpec.class).getIV();
    byte[] ct = ecipher.doFinal(plain);
    byte[] result = new byte[ct.length + iv.length];
    System.arraycopy(iv, 0, result, 0, iv.length);
    System.arraycopy(ct, 0, result, iv.length, ct.length);
    return result;
}

public byte[] decrypt(byte[] encrypt) throws Exception {
    byte[] iv = new byte[dcipher.getBlockSize()];
    byte[] ct = new byte[encrypt.length - dcipher.getBlockSize()];
    System.arraycopy(encrypt, 0, iv, 0, dcipher.getBlockSize());
    System.arraycopy(encrypt, dcipher.getBlockSize(), ct, 0, ct.length);

    dcipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iv));
    return dcipher.doFinal(ct);
}

您需要在初始化步骤中将secret存储在私有变量中，以使解密起作用。

请记住，PBDKF2的盐也应该是随机的，长度为16个字节。您可以将它与IV一起存储。

AES加密密钥生成是否与每次执行一致？

1 个答案: